Testing system



June 11, 1929. D GANNETTH 1,716,438 I v TESTING SYSTEM Filed Sept. 17,. 1927 IN VEN TOR.

' ATTORNEY Patented June 11, 1929.

barren stares titans rarest orricn.

DANFORTH K. eANNn'r'r, or JACKSON HEIGHTS, New YORK, AssIoNon T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION on NEW YORK.

TESTING SYSTEM.

Application filed September 17, 1927. Serial No. 220,135.

This invention relates to electrical systems, and particularly to circuits for testing, calibrating and varying the frequencies of electrical vibrators.

One of the objects of this invention is to provide an arrangement for calibrating the periodicity of avibrator or other source of low frequency oscillations by the agency of a detector device such as telephone recelver, which object may be accomplished by impressing on the detecting device current of a definite frequency interrupted at the periodicity intended for the vibrator and then. adjusting the periodicity of the, v1- brator to equal that intended therefor.

Another object of this invention is to provide a system in which an alternating current of any frequency may be interrupted by a device such as an electrical vibrator at any periodicity, the device such as the vibrator being adjustable so that thealternatcur ant may be i *rruptcd thereby at any periodicity within definite and predetermined limits.

()thcr objects and features of this invention will be better understood from the dctailcd description hereinafter following, when read in connection with the accon1pany ing drawii g' which shows one embodiment of the invention given her in merely for the purpose of illustration.

Referring to the drawing, an electrical vibrator is shown enclosed in a box determined by dotted lines. This electrical Vi- )rator includes a bridge arrangement in which the arms are resistances R and R fixed in magnitude and preferably of equal magnitude, a resistance R, of variable magnitude and an inductance L'of a suitable time constant. One of the diagonals of the bridge includes the winding of a polar relay WV, which, when the bridge becomes unbalanced, controls the movement of an armature A, between fixed contacts a, and 0 This movement controls the polarity of a D. 0. potential which is to be applied to the other diagonal of the bridge, to be described hereinafter. A battery B or other source of direct current potential is connected in series with a variable resistance R The negative terminal of the battery may, if desired, be grounded as shown. To resistances R and 1%,, which may be of any desirable magnitudes, but which are preferably of equal magnitudes, are connected across the terminals of the battery '13 and the varlable res1stance R which are in series relationship. The point common to resistances R and E, is directly connected to the point it which is commonto the arms of the bridge, resistance R and inductance L. The positive terminal of battery B is connected to the fixed contact as, of polar relay W through the variable resistance, R and the negativeterminal of the battery B is directly connected to the fixed contact Z), of said polar relay. The latter diagonal of the bridge includes in parallel relationship with the circuits just described, the winding of another polar relay which similarly controls the movement of an armature A Armature A, may vibrate between contacts a and 1),. A resistance R, may, if desired,

be interposed in series with the winding of polar relay W as shown, in which event the latter diagonal of the bridge lncludes not only the winding of thepolar relay W but also the resistance of definite magnitude R 1 V i A double-pole double-throw switch DP may be thrown to close either contacts 0 an l (Z or contacts 6 and Contacts 0 and cl ar in series with a detecting device shown herei in as a telephone receiver D and a source of alternating current (not shown), connected to the leads S,'prcferably of any frequency,

such as a thousand cycles, interrupted at a definite periodicity, such, for example, as twenty tim per second. The midcontactsof the double-pole double-throw switch DP are in series with armature AL, and fixed contact a, of the polar relay V Contacts 6. and f'of the double-pole double-throw switch are connected in series'with a source of current 0 of any definite frequency and with. a resistance R The source of current 0 may be of anydesired frequency which may be the same as the frequency of the current impressed upon detecting device or telephone receiver D by the source connected to leads S, i. e., a thousand cycle alternating current. Yet 1t 15 to be dlstmctly understood that the frequency of the current of source 0 may have any other value,.within the scope of this invention.

The primary of a transformer T is connected to the source of current 0 through the resistance R The secondary ofthe'transformer T is connected in series with a device M which may be any well known device n'iinated in a resistance for measuring current magnitudes, such, for example, as a thermocouple. The secondary winding of the transformerT is also con nected to an artificial line AL of any well known type, this'artificial line preferably including well known series and shunt resistance elements, The artificial line AL may also be adjustable in its impedance characteristic in order to be suitable in pro viding different losses between the secondary winding of the transformer T and the output circuit P. The artificial line is ter- R, so that the impedance ot'the system may be made equal to the impedance looking into the output circuit P, thereby substantially minimizing losses due to reflection.

As has already been stated, the polar relay WV, an armature A, which is adapted. to vibrate between the fixed contacts a, and 7),. The contact a, is connected to the posi ive terminal of the battery B through the variable resistance R,,, and. the other con tact Z), is connected to the negative terminal of the battery B. Accordingly, the'armature A, is connected to positive battery or negative battery as the armature A, closes contact a, or contact 2),. The potential of the battery B -minus the potential due to the flow of current throughthe resistance R is applied to the terminals of resistances R, and It, in series relationship. Inasmuch as armature A, is connected to point geommon to resistances R, and R, and inasmuch as the point common to resistances R, and. R, is connected to point It common to iii-- ductance L and resistance R,,. current will flow through resistance R, and inductance L, and through resistances R, and R in one direction or the other, depending upon whether armature A, closes contact a, or contact 1),, as will be more fully described hereinafter.

In the arrangement of the apparatus of the vibrator shown herein, current will flow through two parallel paths in, one direction or the other, these paths including resistance R, and inductance L, and resistance R, and resistance R If V a difference of potential exists between point at the {junction of resistance R, and inductance L, and point- ]0 at the junction of resistances R, and R a current will flow in one direction or the other through the winding of the polar relay which will tend to move its armature from one contact to the other, or viceversa. At the same time, current will be established in the winding of the polar relay which will correspondingly vibrate the armature A between the contacts a and 79 The principles underlying the ope ations of the vibrator shown herein will be better understood from the following description:

Let it be assumed that the armature A, of

of the polar relay TV, and resistance 1%,, 7

this current tending to-hold the armature A, against contact a,. This latter current, would, of course, maintain a steady value if the inductance L were not interposed as an arm of the bridge.

Moreover, as soon as armature -A, closes contact a,, a current starts to build up in the circuit of resistance R, and inductance L. Due to the'tnne constant of inductance L, it will take an appreciable length of time for this current to build up to its maximum value. hen the current through inductance L reaches a predetermined value, however, the winding of the polar relay W, will become oppositely polarized, whereupon the armature A will leave contact (1, At the instant that this takes place, the energy stored in the inductance L begins to discharge through the other arms of the bridge and. this discharge current may further aid in leading the armature A, away from contact (6,.

As soon as armature A, closes contact 7),, current will flow through the resistances R, and R, and through resistance R,, the Winding of the polar relay and resist ance R,, in a direction opposite to the direction of current intnese elements when armature A, closes contact a,, as described hereinabove. The current through the winding of the polar relay W, will tend to hold armature A, against contact 1 The potential now applied to inductance L is in a direction opposite to that of the previous instance, so that thecurrent residing in inductance L begins to decay until it falls to zero and then begins to build up in the opposite direction. As current through the inductance L reaches a predetermined value (in the opposite direction), the armature A, of the polar relay lV, will leave contact 1),.

Again the energy stored inc the magnetic field of "he inductance L will be discharged,

and so it continues.

It is to be observed that as the potential its contacts, such as (L2, to the other of its contacts 6 and vice versa. Resistance R 1s interposed 1n the path lncluding the winding of the polar relay W in order that the current flowing th'erethrough may be,

controlled in magnitude. The vibration of armature A, between contacts a, and b, may

be employed as a means for interrupting an.

The potential of the direct current source B, may, as is well known, vary between definite limits,depending upon the state of charge of the source. Obviously, as the charge ofthe source decreases, the potential thereof will normally decrease so that a smaller current may normally be established through resistance of a definite magnitude. In order to overcome the defects in operation which may be introduced by a varying potential in the source,the resistance R, in series therewith is made adjustable." As the source becomes discharged, thereby decreasing its normal operating potential, the magnitude of the resistance B, may be decreased and, conversely, as the potential of the source increases, the magnitude of the resistance B, may be increased.

It is also to be observed that resistance R, is 'ariable, this resistance controlling the periodicity of the vibrator. As the magnitude of the resistance R, is increased in value, a smaller current flows therethrough and, consequently, a briefer period of time is required for the current through inductance L to reach a value suflicient to bring about the operation of the polar relay V It is therefore apparent that, as the resistance R, is increased in magnitude, the periodicity of the VlbIZLtOI is also increased and, as the resistance R, is decreased in magnitude, the periodicity of the vibrator is correspondingly decreased. The polar relay lV, brings the armature A, in vibration at the established periodicity of the vibrator;

It is also to be noted that by changing the magnitude of resistance R, from one value to another, the perlodicity of the vibrator may be changed from one frequency to an other frequency. In other words, if the resistance B, were adjusted to establish a frequency of, for example, twenty cycles, then by decreasing the magnitude of resistance R, by a definite amount, the periodicity of the vibrator may be changed to, for example, sixteen cycles.

To calibrate the vibrator with respect. to frequency, the double-pole double-throw switch DP should be thrown so as to close contacts 0 and (Z. As has already been stated, a source of alternating current of, for example, one thousand cycles and an interrupter for interrupting this alternating current at a definite period, for example, twenty times per second, become connected to the leads S. By so throwing switch DP,

the armature A, and contact a will then be in series with the detector or telephone receiver D and with the leads S. Ifthe frequency of vibrationof the vibrator does not equal the frequency of interruption of the source connected to the leads S, beats will be heard 1n the detecting device or telephone receiver D. By varying the magnitude of the resistance It, in the bridge of the vibrator, it becomes possible to bring the fre quency of the vibrator very closely to the frequency of interruption of the source connected to the leads 8. Of course, by changing the magnitude of the resistance R, by a j definite amount, the frequency ofthe vibrator may be changed b; amount, as has already been stated.

When the-switch DP closes contacts 6 and f, then the armature A, and contact a becomeconnected in series with the'source of alternating current 0 and with the resistance R In this event, the current of source 0 will be inteii'rupted in accordancewith the frequency of vibration of armature A i. 'e., the'ilfrequency of the vibrator. Inasmuch as the source() is connected to the trans former T, current of the source .0, as inte'rrupted'by the armature A, of polar relay W will be transmitted to the output circuit 1 through the artificial line AL and the terminating resistance 11,. The magni* tude of resistance R, should be such that the I device M will indicate that current of the proper magnitude is being transmitted'to the output circuit P through the artificial line AL and terminating resistance R,. The resistance R, functions also to prevent the destruction of the armature of agenerator dueto the flow. of'current of an excessive valuetherethrough.

It will thus beapparent that by manipulating switch DP to close contacts a and d,

justed to the samevalue as that of aninterthe frequency of the vibrator may be ad a rupter connected to'lead's-S. In the particu I lar illustration given herein, the frequency of the vibrator is made to equal the fr'equency of interruption of an alternating current source. Moreover, by having switch DP close contacts 6 and f, an arrangement iseflected for interrupting current of the same frequency or of a di'lferent frequency at the periodicity of the Vibrator. Such an interrupted current may be used, for example, for testing purposes 'in voice fre quencytoll ringing circuits.

While this invention has been shown in one particular embodiment merely for the purpose of illustration, it is to be distinctly understood that the general principles of this invention may be applied to other and widely varied organization without departing from the spirit of the invention or the scope'of the appended claims.

lVhat is claimed is: l. The method of calibrating the per1od1city of a vibrator by means of a detecting device, which consists in impressing on said detecting devicejcurrent of a definite frequency interrupted at the periodicity intended for the vibrator, and adjusting the periodicity of the vibrator to equal the periodicity intended therefor. Y

2.. The method. of calibrating a vibrator of adjustable periodicity to a predetermined periodicity, which consists in transmitting current of definte frequency, interrupting the current of definite frequency at the predetermined periodicity, and bringing the v1.-

' brator to a periodicity equal to the periodic:

ity of interruption of the transmitted current.

3. The method of bringing a vibrator of adjustable periodicity to a predetermined periodicity, which consists in interrupting current of a definite frequencyat the predetermined periodicity, and changing the periodicity of the vibrator equal to the predetermined periodicity of interruption of said current. v I r 4. The method of bringin g'a vibrator of adjustable periodicity to a predetermined periodicity, Which consists in interrupting current of definite frequency at the predetermined periodicity, determining Whether in, synchronism With the predetermined periodicity.

6. The method of adjusting the vibratory terrupting the impression of said alternating current on said electrical circuit at the predetermined periodlcity, opening and closing the electrical circuit at the period, of

said Vibrating element, and adjusting the vibratory period of said vibrating element until 1n synchronism with the predeter- -mined periodicity.

7. The method of adjusting the Vibratory. 7

period of a vibrating element to apredetermined perlodlcity, which consists 1n impressing on an electrical circuit an alternating current of definite frequency, interrupting the impression 7 of said alternating current on said electrical circuit at the predetermined periodicity, opening and closing the electrical circuit at the period of said vibrating element, and indicating Whether the vibratory period of said vibrating element equals the predetermined period.

8. The method'of adjusting the vibratory period of a vibrating element to a predeter mined periodicity, Which consists in impressing on. an electrical circuit an alternating current of definite frequency, interruptii'rg the impression of said alternating current on said electrical circuit at the predetermined periodicity, opening and closing the electrical circuit at the period of said vibrating element, indicating Whether the vibratory period of said vibratingelement equals the predetermined period, and-adjusting the vibratory period of said vibrat ing element so as to be synchronous with the predetermined periodicity.

In testimony whereof, I have signed my name to this specification this 16th day of September, 1927. N

DANFORTI-I K. GANNETT. I 

